Fiber-based interferometer system for monitoring an imaging interferometer

Abstract

Apparatus include a microscope including an objective and a stage for positioning a test object relative to the objective, the stage being moveable with respect to the objective, and a sensor system, that includes a sensor light source, an interferometric sensor configured to receive light from the sensor light source, to introduce an optical path difference (OPD) between a first portion and a second portion of the light, the OPD being related to a distance between the objective lens and the stage, and to combine the first and second portions of the light to provide output light, a detector configured to detect the output light from the interferometric sensor, a fiber waveguide configured to direct light between the sensor light source, the interferometric sensor and the detector, a tunable optical cavity in a path of the light from the sensor light source and the interferometric sensor, and an electronic controller in communication with the detector, the electronic controller being configured to determine information related to the OPD based on the detected output light.

1. An apparatus, comprising:
 a microscope comprising an objective and a stage for positioning a test object relative to the objective, where the stage is moveable relative to the objective and the microscope images the test object using the objective; and 
 a sensor system configured to monitor a relative position between the objective and the stage, the sensor system comprising:
 a sensor light source; 
 an interferometric sensor configured to receive light from the sensor light source, to introduce an optical path difference (OPD) between a first portion and a second portion of the light, the OPD being related to the relative position between the objective and the stage, and to combine the first and second portions of the light to provide output light; 
 a detector configured to detect the output light from the interferometric sensor; 
 a fiber waveguide configured to direct light between the sensor light source, the interferometric sensor and the detector; 
 a tunable optical cavity in a path of the light from the sensor light source and the interferometric sensor; and 
 an electronic controller in communication with the detector, the electronic controller being configured to determine information related to the relative position between the objective and the stage based on the detected output light. 
 
 
     
     
       2. The apparatus of  claim 1 , wherein the electronic controller is configured to adjust a focus of the microscope relative to the test object based on the information. 
     
     
       3. The apparatus of  claim 1 , wherein during operation the apparatus determines information about the test object using the microscope, where determining the information about the test object includes reducing errors due to vibrations in the apparatus using the information determined by the electronic controller. 
     
     
       4. The apparatus of  claim 1 , wherein the microscope is an interferometric microscope. 
     
     
       5. The apparatus of  claim 4 , wherein the interferometric microscope is a scanning white light interferometry (SWLI) microscope. 
     
     
       6. The apparatus of  claim 4 , wherein the interferometric microscope is a pupil plane SWLI microscope. 
     
     
       7. The apparatus of  claim 4 , wherein the interferometric microscope is configured to determine information about a test object positioned on the stage by illuminating the test object with test light and to combining the test light with reference light from a reference object to form an interference pattern on a detector, wherein the test light and reference light are derived from a common source, and the apparatus is configured to reduce uncertainty in the information about the test object due to scan errors based on the information determined by the electronic controller. 
     
     
       8. The apparatus of  claim 1 , wherein the sensor system comprises one or more additional interferometric sensors each configured to receive light from the sensor light source. 
     
     
       9. The apparatus of  claim 8 , wherein each interferometric sensor is configured to introduce an OPD between two components of its corresponding light, each OPD being related to a corresponding displacement between the objective and the stage along a corresponding axis. 
     
     
       10. The apparatus of  claim 9 , wherein the electronic controller is configured to determine information about a tilt of the stage relative to the objective based on determining information related to the corresponding OPD for at least two of the interferometric sensors. 
     
     
       11. The apparatus of  claim 8 , wherein the sensor system comprises one or more additional detectors, each configured to receive output light from a corresponding interferometric sensor. 
     
     
       12. The apparatus of  claim 11 , wherein each additional interferometric sensor receives light from the sensor light source and directs output light to its corresponding sensor through a corresponding fiber waveguide. 
     
     
       13. The apparatus of  claim 11 , wherein the tunable optical cavity is in the path of the light from the sensor light source to each interferometric sensor. 
     
     
       14. The apparatus of  claim 1 , wherein the interferometric sensor comprises a lens positioned to receive light exiting the fiber waveguide and to focus the light to a waist. 
     
     
       15. The apparatus of  claim 14 , wherein the lens is a graded index lens. 
     
     
       16. The apparatus of  claim 14 , wherein the lens is attached to the objective. 
     
     
       17. The apparatus of  claim 14 , wherein the lens is attached to the stage. 
     
     
       18. The apparatus of  claim 1 , wherein the microscope comprises a microscope light source and the objective comprises one or more optical elements, the microscope being configured to deliver light from the microscope light source to the test object and the one or more optical elements being configured to collect light from the test object, and the interferometric sensor is configured to direct light to the stage through the one or more optical elements of the objective. 
     
     
       19. The apparatus of  claim 1 , wherein the sensor light source is a broadband light source. 
     
     
       20. The apparatus of  claim 1 , wherein the sensor light source has a peak intensity at a wavelength in a range from 900 nm to 1,600 nm. 
     
     
       21. The apparatus of  claim 1 , wherein the sensor light source has a full-width at half maximum of 50 nm or less. 
     
     
       22. The apparatus of  claim 1 , wherein the sensor light source has a coherence length of about 100 microns or less. 
     
     
       23. The apparatus of  claim 1 , wherein the tunable optical cavity comprises two optical paths for the light, each path comprising a fiber stretcher module. 
     
     
       24. The apparatus of  claim 1 , wherein the sensor light source and the detector are located in a housing separate from the microscope. 
     
     
       25. The apparatus of  claim 1 , wherein the information is about a displacement between the objective lens and the stage along an axis. 
     
     
       26. The apparatus of  claim 25 , wherein the microscope is configured to scan the stage parallel to the axis. 
     
     
       27. The apparatus of  claim 25 , wherein the information is about an absolute displacement between the objective lens and the stage. 
     
     
       28. The apparatus of  claim 25 , wherein the information is about a relative distance between the objective lens and the stage. 
     
     
       29. The apparatus of  claim 1 , wherein the microscope comprises a microscope light source and is configured to deliver light from the microscope light source to a test object located on the stage, wherein a wavelength of peak intensity of the microscope light source is about 100 nm or more from a wavelength of peak intensity of the sensor light source. 
     
     
       30. The apparatus of  claim 29 , wherein the wavelength of peak intensity of the microscope light source is in a range from 300 nm to 700 nm and the wavelength of peak intensity of the sensor light source is in a range from 900 nm to 1,600 nm. 
     
     
       31. A system, comprising:
 the apparatus of  claim 1 ; 
 one or more additional microscopes each comprising a corresponding objective and a corresponding stage, 
 wherein the sensor system comprises one or more additional interferometric sensors each associated with one of the one or more additional microscopes, each additional interferometric sensor being configured to receive light from the sensor light source. 
 
     
     
       32. The system of  claim 31 , wherein each of the one or more additional interferometric sensors is configured to introduce an optical path difference (OPD) between a first portion and a second portion of the light from the light source, the OPD being related to a relative position between the objective and the stage of the microscope with which the sensor is associated, and to combine the first and second portions of the light to provide output light. 
     
     
       33. The system of  claim 32 , wherein the sensor system comprises one or more additional detectors, each configured to detect the output light from a corresponding one of the additional interferometric sensors. 
     
     
       34. The system of  claim 31 , wherein the sensor system comprises one or more fiber waveguides configured to direct light between the sensor light source and the one or more additional interferometric sensors. 
     
     
       35. The system of  claim 31 , wherein each of the microscopes is arranged to inspect a different test object.